1. Chapter Overview
Network Communications

2. Signals and Protocols
A data network is a group of computers connected by some network mediums.
The network medium carries signals between computers.
Signals reduce complex information to the simplest possible form.
Computers communicate by following rules defined in a protocol.

3. Protocol Services Packet acknowledgment Segmentation Flow control
Error detection
Error correction
Data compression
Data encryption

4. Local Area Networks
A local area network (LAN) is a collection of computers located in a relatively small area.
The pattern in which computers in a LAN are connected is called the topology.
The basic LAN topologies include bus, star, and ring.

5. Wide Area Networks (WAN)
WANs connect LANs through routers
Figure 1.3 gives another example

6. Three Common Network Components
Servers – a power computer providing services and runs an NOS
File, Mail, Web, Printer, Fax, App, Telephone, etc.
Workstations – not necessary a client machine, but have resources to provide.
In Unix world, a workstations has storage spaces to share
Hosts – network devices with an IP address, can be a server, workstation, or others

7. Virtual LANs and Virtual Private Networks
A virtual LAN (VLAN), is a group of hosts communicate as if they were on the same broadcast domain, regardless of their physical location. A VLAN has the same attributes as a physical LAN, but it allows for end stations not located on the same network switch. Network reconfiguration is done through software (more on chapter 11, if we go that far).
A virtual private network (VPN) is a network that uses a public telecommunication infrastructure, such as the Internet, to provide secure access to a user’s intranet (more on chapter 13, if we get that far).

8. Client/Server and Peer-to-Peer Networking
Clients request services; servers provide services
On a client/server network, computers function as either clients or servers.
On a peer-to-peer network, computers can function as both clients and servers.
Microsoft Windows, UNIX, and Linux are peer-to-peer network operating systems.
Novell NetWare is a client/server network operating system.

9. Cable Topologies
Bus
Star
Ring
Hierarchical star
Mesh
Wireless

10. Bus Topology

11. Star Topology

12. Ring Topology

13. Ring Network Types
Physical ring
Logical ring
Double ring (FDDI)

14. Hierarchical Star Topology

15. Mesh LAN Topology

16. Mesh Internetwork

17. Wireless Topologies
Ad hoc topology: Connects two or more wireless computers communicating with each other only
Infrastructure network: Connects wireless computers communicating with a network access point that provides access to a standard cabled network

18. Others Hybrid Point-to-point Point-to-multipoint
Physical start, logical rain or bus
Point-to-point
Point-to-multipoint

19. Topology selection consideration
Cost
Ease of installation
Ease of maintenance
Fault-tolerance requirement
Coverage area
Security, etc.

20. Backbone Network
Could be Switches